I would most definitely use pipe cleaners as they easily can be bent into a double helical shape. As for the phophate groups and the deoxyribose sugars, why not use objects around the house like paper clips which you can bend into a carbon ring to make the deoxyribose and you can use buttons or bottle caps for the phosphate groups? As for the nitrogenous bases, pipe cleaners of different colors can represent the adenine, guanine, cytosine and thymine. Remember that A pairs with T and C pairs with G. Modeling clay seems to be a good idea, however, why not make your own clay with food coloring and flour and water? That stuff will definitely air dry. Cardboard, kinects, and even beads or costume jewelry can be used to make your model. Use your imagination and look around the house for items that can be used.
hi, you can use the particle flow for the making 3d dna animation with 3d max.
You can also try modular origami. In modular origami, you make small pieces (think of them like building blocks) that fit perfectly into other small pieces. You can sort of sculpt the small pieces into any larger shape you want. I used modular origami to make a 3d model of the stone pyramids in South America. The smaller the paper you use, the better the model will look. It can be time consuming but if you plan it nicely, you'll have a superb model.